Dale & Lewis Chapter 3 Data Representation

Representing color Similarly to how color is perceived in the human eye, color information is encoded in combinations of intensities of red, green and blue colors. Monitors Printers Scanners…

Color depth Similar to an audio channel, each color channel can be represented by n bits  more bits, more levels If each channel uses 8 bits (256 levels), then a color uses 24 bits  TrueColor (16+ million colors) More than the human eye can distinguish or hardware reproduce

Images Now that there is a way to represent color, an image can be constructed with an array of picture elements (pixels) Pixel resolution (how many pixels or dots per inch - dpi) and color depth determine the quality of an uncompressed image

Image file formats and compression BMP – popular bitmap, lossless but can use run-length encoding to reduce file size GIF (Graphics Interchange Format) – can include an index of colors to reduce file size (i.e. if fewer than 16M+ colors are needed, reduce bits needed for each channel  index converts reduced bit encoding to RGB) −A version of GIF defines different frames that can be played back as animation JPEG (Joint Picture Experts Group) – lossy perceptual compression to exploit the eye’s sensitivity to gradual color changes  average color hues over short distances PNG (Portable Network Graphics) – a GIF replacement with broader color depth

Graphics Line art and graphics may contain a lot of empty space and bitmaps are not optimal representations Vector graphics store images as collection of colored lines and shapes −Collection of commands −Complexity determines file size −Resizing can be done with perfect rendering and without loss of information  SVG file format (Scalable Vector Graphic)

Video Timed frame sequence (24 or 30 fps)  very large files Complex information  difficult compression Codec (COder/DECoder) define how to interpret bits Can be processor-intensive processes  some codecs require specialized hardware Temporal compression −Keyframe + delta frames Spatial compression −Groups similar areas of a frame into a large pixel, or compresses frames just as in image files

Dale & Lewis Chapter 4 Gates and Circuits

Computers & Electricity Voltage: measure of electrical potential difference −Analogy: water pressure in a garden hose Voltage is variable: for binary representation we only look at off states (low or no voltage) and on states (high voltage, i.e. 5V) Thresholds used to deal with noise: off states (0  2V), on states (2V  5V) Maximum voltage set to prevent damage and for power/speed considerations

Gates Device that performs a basic operation on electrical signals One or more input signals produces one output signal Basic operations: NOT, AND, OR Other convenient operations: XOR, NAND, NOR Circuits −Combination of interacting gates designed to accomplish a specific logic function −E.g. perform arithmetic, store values

Notations to describe behavior of gates and circuits Boolean algebra −Variables can take only values of 0 and 1 −Powerful way to demonstrate the activity of circuits Logic diagrams −Graphical representation of a circuit −Each gate is represented by a specific symbol Truth tables −Describes the function of a gate or circuit −Lists all possible input/output combinations

Gates Six main gate types Can build anything we need from them −Boolean algebra operations: AND, OR, NOT −Convenient: XOR, NAND, NOR −Easier to physically build a NAND gate than AND gate See Chapter 4 slides from the Book…